Top Opinion

Let them cry until you can safely pull over and handle it. Crying for a few minutes isn't going to hurt them, but trying to comfort a crying infant while piloting a ton of deadly machinery has a better than average chance of possibly killing them when you lose focus and plow into oncoming traffic or something. Which would you rather have, a crying infant or a dead one?

Pull over and nurse them some or give them some water...make sure they are clean and dry...and nothing is pinching them...and the sun is not beating them in the face..then give them a paci and something to kick.
Then get going.

Honestly, the best you can do is to get somewhere that you can stop and deal with the child. Usually, if they are crying in the car, that means they either dropped binky, are hungry, or need to be changed. I left tired out because all 3 of mine would fall asleep in the car if that was the problem.

Let them cry until you can safely pull over and handle it. Crying for a few minutes isn't going to hurt them, but trying to comfort a crying infant while piloting a ton of deadly machinery has a better than average chance of possibly killing them when you lose focus and plow into oncoming traffic or something. Which would you rather have, a crying infant or a dead one?